问题
单项选择题
在数据库逻辑设计中，当将E—R图转换为关系模式时，下面的做法( )，是不正确的。
A．一个实体类型转换为一个关系模式
B．一个联系类型转换为一个关系模式
C．由实体类型转换成的关系模式的主键是该实体类型的主键
D．由联系类型转换成的关系模式的属性是与该联系类型相关的诸实体类型的属性的全体
答案
参考答案：B
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在数据库逻辑设计中，当将E—R图转换为关系模式时，下面的做法( )，是不正确的。
A．一个实体类型转换为一个关系模式
B．一个联系类型转换为一个关系模式
C．由实体类型转换成的关系模式的主键是该实体类型的主键
D．由联系类型转换成的关系模式的属性是与该联系类型相关的诸实体类型的属性的全体
参考答案：B
Foods quickly spoil and break down if they are not stored correctly. Heat and damp encourage increase in micro-organisms(微生物的), and sunlight can vitamins in such food as milk. Therefore, most foods should be stored in a cool, dark and dry place. Some foods _ bad quickly, such as meat, eggs and milk. They should be stored in a temperature of 5°C~10°C. In this temperature range, the activity of micro-organisms is _ . In warm climates, this temperature can be kept _ in a fridge or in the underground basement(地下室) of a house. Dry goods, such as flour and rice, should be kept at a slightly higher temperature. A temperature of 15°C is ideal. In Britain and northern European countries this means that the room in which dry foods are stored should the general heating of the house. The room should also be well and, above all, dry. Damp very quickly causes the of the green molds. These molds often grow on cheese if it is not stored properly. Fruits and vegetables need cool and damp _ , so an underground basement usually _ an excellent storage place. If the central heating unit is in the basement, _ __, it will not be ideal unless the unit and the pipes(管道) do not give out any heat.
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